A hard magnetic disk drive (HDD) is often used as an auxiliary mass data storage device for a computer. Saitoh, Scanning Memory Device, Japanese patent application no. 6-270297 discloses a scanning-type data storage system that is used as a substitute mass data storage device for an HDD. Such mass data storage system occupies a much smaller volume than an HDD, while providing both significantly faster access speeds and higher storage densities.
A scanning-type data storage system reads or writes data by applying electrical stimuli to a data storage medium with a plural data read/write access probes. Both a read operation and a write operation performed by a probe constitute access operations. The useful life of this type of mass data storage system is limited by wear of the probes and the wear of storage medium. Thus, the number of access operations to the storage medium by the probe is limited by probe wear, and is also limited by wear of the storage medium.
In a scanning-type data storage system, the maximum number of access operations that each probe can perform is the same, and the maximum number of access operations that each storage area can receive is the same. However, the probes perform access operations different frequencies, and the storage areas receive access operations at different frequencies. For example, the data stored in some of the storage areas may be read much more frequently than the data stored in other storage areas, and the data stored in some of the storage areas may be rewritten much more frequently than the data stored in others of the storage areas.
Some probes perform many access operations and therefore reach their limit counts for access operations sooner than other probes. In contrast, because some probes perform few access operations, these probes can continue to be useful until reaching their limit counts for access operations, even if the access operations performed by other probes have reached their limit counts. Similarly, because some storage areas receive many access operations, they reach their limit counts for access operations sooner than other storage areas that receive few access operations. In contrast, some storage areas receive few access operations and can continue to be useful long after the storage areas that received many access operations have reached their limit counts for access operations.
A conventional scanning-type data storage system can therefore reach the end of its useful life and become useless, even though many probes and many storage areas have not reached their limit counts for the access operations. Thus, a conventional scanning-type data storage system can reach the end of its useful life without wearing out all of its probes or all of its storage areas.
In Saitoh, probes that have reached a predetermined number of access operations, i.e., their limit count, are considered to be unavailable, and the data in the storage area that is accessed by an invalid probe are transferred to a spare storage area. However, the spare storage areas are sometimes rapidly exhausted. The data storage system reaches the end of its useful life when all of the spare storage areas are used, and any probe again reaches the limit count for access operations.
While the prior-art provides some ways of extending the useful life of a data storage system, the prior art fails to provide ways to extend the useful life of the data storage system when the limits on the number of access operations of the probes and/or to the storage medium have been reached. The development of a system overcomes these limitations would constitute a major technological advance.